The death toll from deadly tornadoes and severe flooding that struck Oklahoma on Friday and Saturday has risen to 18, including 12 adults and six children, with the bodies of seven people still unidentified, the state's chief medical examiner said on Monday.

The storms also caused flash flooding throughout the Oklahoma City area. The Oklahoma County Sheriff's department said it conducted several water rescues on Friday and Saturday, helping dozens of people victimized by the flooding.

A 64-year-old man drowned on Saturday morning when he drove off a washed-out bridge in eastern Oklahoma County. His body was recovered a quarter-mile from where his vehicle was found, the sheriff's department said.

Of the 18 confirmed fatalities, nine were in Oklahoma City, while six were in its western suburbs - four in El Reno and two in Union City. The communities of Luther, Wewoka and Clearview, communities east of Oklahoma City, each recorded one fatality.

Friday's spate of tornadoes landed just 11 days after a massive EF5 tornado, the most powerful rating, tore into Oklahoma City and its suburb of Moore, killing 24 people. Moore sustained limited damage in Friday's storms.

The death toll was expected to rise, an Oklahoma medical examiner's office spokeswoman said. More than 120 people were being treated at hospitals, including about 70 children. Some were in critical condition.

The storm — less than 1 per cent of all tornadoes reach such wind speed — ripped through scores of buildings in the suburb of Moore in a region of the US known as Tornado Alley. Block after block lay in ruins. Cars and trucks were left crumpled.

The National Weather Service estimated that the tornado reached up to a half-mile (.8 kilometers) wide and was an EF-4 on the enhanced five-point Fujita scale, the second most powerful type of twister.

A monstrous tornado of rare power roared through an Oklahoma City suburb, killing at least 51, flattening neighborhoods with winds up to 200 mph (320 kilometers) and destroying at least one school. Officials said children were among the dead.

James Rushing, who lives across the street, heard reports of the approaching tornado and ran to the school, where his 5-year-old foster son, Aiden, attends classes. Rushing believed he would be safer there.

A monstrous tornado of rare power roared through an Oklahoma City suburb, killing at least 51, flattening neighborhoods with winds up to 200 mph (320 kilometers) and destroying at least one school. Officials said children were among the dead.

The death toll from deadly tornadoes and severe flooding that struck Oklahoma on Friday and Saturday has risen to 18, including 12 adults and six children, with the bodies of seven people still unidentified, the state's chief medical examiner said on Monday.